Multispectral sensors can acquire images of an object under a plurality of distinct illumination and/or imaging conditions. Images from multispectral sensors can be used for various purposes such as for biometric imaging, bar code reading and authentication, documentation authentication, and quality assurance, to name a few.
Conventional optical fingerprint sensors typically incorporate a single total internal reflectance (TIR) imager, which can require that a number of conditions be met to provide a good fingerprint image. These conditions can include the requirement that the fingerprint ridges are intact, clean, in optical contact with the sensor surface, and that the skin is of proper moisture content, i.e., neither too dry nor too wet. If any of these conditions aren't met, the resulting fingerprint image can be degraded or even missing entirely. However, when these conditions are met, the resulting image is generally of high quality and useful for both automated analysis and analysis by a human observer.
Multispectral sensors and others based on direct imaging can acquire images under a much broader range of conditions of the skin, the local environment, and the nature of the interface between the skin and sensor. However, such images are generally of lower contrast than the corresponding TIR image, if the TIR image is of high quality.
It can be a time consuming process for a sensor to illuminate and acquire images from the plurality of distinct optical and/or imaging conditions. Multispectral sensors often have difficulty determining when an object is properly placed at the sensor for imaging, determining whether an object is a proper object for imaging, and/or distinguishing between an object for imaging and background objects.